The present invention relates to an inverted portal axle configuration which provides for a vehicle having a low floor.
Mass transit vehicles, such as trolley cars, buses, and the like typically have seats aligned at the lateral sides of the vehicle, with a central aisle and floor extending along the vehicle. In order to facilitate entering and exiting from the vehicle, it is desirable to have the vehicle floor and aisle positioned relatively low to the ground. This provides faster cycle time at bus stops.
Many such vehicles provide a rigid axle having a gear box at each longitudinal end to form an inverted portal axle configuration. The inverted portal axle configuration is particularly effective in providing a low floor vehicle.
In the inverted portal axles, the axle shafts are offset vertically relative to the wheel axis by a specific distance, the so-called axle shaft drop. That is, the axle shaft drop is the offset between the wheel axis and the axle shaft axis. This drop is limited by a side reduction gear system. Based on the existing twin idler gear concepts, this distance is approximately 140-150 mm.
Larger distances may be difficult to achieve due to the very large size of the idler gears, which would be expensive and difficult to package properly, due to wheel, brake, and suspension constraints. As result of this, an axle beam drop of approximately 110 mm has been achieved by conventional products. That is, the axle beam drop is the offset between the wheel axis and the top of the center housing. However, on an ultra low floor vehicle, this requires a ramp on the vehicle floor over the drive axle to allow the vehicle to meet the floor in the rest of the vehicle and at the doors. Slopes in the range of 8 to 12 degrees are typical but are considered excessive; therefore, a larger axle beam drop is desired.
Accordingly, it is desirable to provide an inverted portal axle configuration that provides for an ultra low flow profile while minimizing the ramp angle on the vehicle floor over the drive axle.